Just to put things in perspective I found 2 calculators that convert FPS to MPH. I use both and the answers were the same. I rounded off to 4 numbers after the decimal point.
1400 FPS = 954.5455 MPH
1550 FPS = 1056.8182 MPH
Ducks normally fly between 40 and 60 MPH, a canvassback was once clocked at 72 mph and a red breasted merganser was once clcked at 100 mph. No duck comes close to approaching the speed of shot, lead or steel. In the grand scheme of things, so long as you swing through the duck and shoot when you ass the bill or if you have mastered the sustained lead method of shooting, I prefer the first, method, the speed of the shot doesn't mean a whole lot, knowing how to wing shoot means a whole lot more.